Microelectronic devices, such as semiconductor devices, imagers, and displays, are generally fabricated on and/or in microelectronic workpieces using several different types of machines (“tools”). Many such processing machines have a single processing station that performs one or more procedures on the workpieces. Other processing machines have a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. In a typical fabrication process, one or more layers of conductive materials are formed on the workpieces during deposition stages. The workpieces are then typically subject to etching and/or polishing procedures (i.e., planarization) to remove a portion of the deposited conductive layers for forming electrically isolated contacts and/or conductive lines.
Tools that plate metals or other materials on the workpieces are becoming an increasingly useful type of processing machine. Electroplating and electroless plating techniques can be used to deposit copper, solder, permalloy, gold, silver, platinum, electrophoretic resist and other materials onto workpieces for forming blanket layers or patterned layers. A typical copper plating process involves depositing a copper seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, a blanket layer or patterned layer of copper is plated onto the workpiece by applying an appropriate electrical potential between the seed layer and an anode in the presence of an electroprocessing solution. The workpiece is then cleaned, etched and/or annealed in subsequent procedures before transferring the workpiece to another processing machine.
FIG. 1 illustrates an embodiment of a single-wafer processing station 1 that includes a container 2 for receiving a flow of electroplating solution from a fluid inlet 3 at a lower portion of the container 2. The processing station 1 can include an anode 4, a plate-type diffuser 6 having a plurality of apertures 7, and a workpiece holder 9 for carrying a workpiece 5. The workpiece holder 9 can include a plurality of electrical contacts for providing electrical current to a seed layer on the surface of the workpiece 5. When the seed layer is biased with a negative potential relative to the anode 4, it acts as a cathode. In operation, the electroplating fluid flows around the anode 4, through the apertures 7 in the diffuser 6, and against the plating surface of the workpiece 5. The electroplating solution is an electrolyte that conducts electrical current between the anode 4 and the cathodic seed layer on the surface of the workpiece 5. Therefore, ions in the electroplating solution plate the surface of the workpiece 5.
The plating machines used in fabricating microelectronic devices must meet many specific performance criteria. For example, many plating processes must be able to form small contacts in vias or trenches that are less than 0.5 μm wide, and often less than 0.1 μm wide. A combination of organic additives such as “accelerators,” “suppressors,” and “levelers” can be added to the electroplating solution to improve the plating process within the trenches so that the plating metal fills the trenches from the bottom up. As such, maintaining the proper concentration of organic additives in the electroplating solution is important to properly fill very small features.
One drawback of conventional plating processes is that the organic additives decompose and break down proximate to the surface of the anode. Also, as the organic additives decompose, it is difficult to control the concentration of organic additives and their associated breakdown products in the plating solution, which can result in poor feature filling and nonuniform layers. Moreover, the decomposition of organic additives produces by-products that can cause defects or other nonuniformities. To reduce the rate at which organic additives decompose near the anode, other anodes such as copper-phosphorous anodes can be used.
Another drawback of conventional plating processes is that organic additives and/or chloride ions in the electroplating solution can alter pure copper anodes. This can alter the electrical field, which can result in inconsistent processes and nonuniform layers. Thus, there is a need to improve the plating process to reduce the adverse effects of the organic additives.
Still another drawback of electroplating is providing a desired electrical field at the surface of the workpiece. The distribution of electrical current in the plating solution is a function of the uniformity of the seed layer across the contact surface, the configuration/condition of the anode, the configuration of the chamber, and other factors. However, the current density profile on the plating surface can change during a plating cycle. For example, the current density profile typically changes during a plating cycle as material plates onto the seed layer. The current density profile can also change over a longer period of time because (a) the shape of consumable anodes changes as they erode, and (b) the concentration of constituents in the plating solution can change. Therefore, it can be difficult to maintain a desired current density at the surface of the workpiece.